Such a method is known, for example, from WO 2007/079894 A1. In this method, an optical waveguide is supplied to a container of a converter, which receives molten metal. The task of the optical waveguide is to guide the electromagnetic radiation of the molten metal to an optical detector. A line through which fluid is flowed is arranged between the optical detector and the container, in which line the optical waveguide is guided and in which the optical waveguide is transported with the aid of the fluid. In one preferred embodiment, the invention comprises a reeling device, which successively reels off the optical waveguide from a stock. This is necessary because the high temperatures at the measurement point cause the optical waveguide to gradually melt at its end immersed in the molten metal and to require corresponding infeeding. If the optical waveguide has been entirely consumed, a new optical waveguide must be used.
In order to obtain reliable measurement values, such a method requires a calibration of the measuring device (test equipment) prior to the measurement, in particular after introduction of a new optical waveguide. In a calibration, the measurement value of test equipment (test value) is compared with the measurement value of a measurement standard (calibration value). If the difference between the test value and the calibration value is unacceptably large, an adjustment occurs. This involves setting or adjusting the measuring device in order to eliminate the systematic deviation to the extent required for the intended application. After the adjustment, another calibration must be realized. These steps must, if necessary, be repeated until an acceptable deviation is obtained. Measuring devices which have small measurement deviations are advantageously used as measurement standards.
Measurement standards usually require, in addition to the already existing measuring devices, additional access to the molten metal in order to determine the temperature. It is known, for example, that measuring rods with thermal elements mounted at the ends are introduced into the molten metal. This type of measurement is used, for example, in the converter process for steel production. The disadvantage of this is that the process must be interrupted. The period of time required for the temperature measurement and the corrective measures decided upon on the basis thereof complicates process control and the process sequence and thus has a negative impact on the steel quality.
Alternatively, pyrometers are used as measurement standards in order to determine the temperature in a molten metal. It is known from practical experience, for example, to realize a pyrometric analysis of the electromagnetic radiation emitted by the chalybeate bath for the purpose of continuous in situ temperature measurement. The surface of the chalybeate bath is thus observed for example. In this method, however, considerably fluctuating emissivity of the heterogenous and greatly agitated bath surface leads to unacceptable measurement uncertainty.
The provision of fixtures, such as windows, for example, in the fire-proof lining of a converter wall has also been considered. However, they are associated with disadvantages due to the optical degeneration caused by the high temperatures, which can typically reach as much as 1800° C. Access means provided in the fire-proof lining are also subject to significant mechanical stress as a result of settling processes, which deform the usually tube-shaped means of access to the molten mass to such an extent that an optical access to the chalybeate bath along the line of sight is no longer possible.
Such disadvantages are not restricted only to the converter process, but extend to almost all processes with molten metal. This might include, for example, the continuous casting process and the problematic accessibility to measurement points in the distribution trough, the immersion tube or in the permanent mold. Frequently, accessibility to certain measurement points is not possible generally or, for example for process-related reasons, at certain times.